The studies proposed here will compare the expression of the principal chymotrypsin-like proteases of human mast cells in normal and inflamed airway tissues and will characterize genetic and nuclear elements responsible for their regulated expression. These enzymes, chymase and cathepsin G, are major components of secretory granules in the MC/TC subset of mast cells. They have potent secretagogue, peptidase and matrix-degrading activity and are released into the extracellular milieu following activation of mast cells by antigen-bound IgE, neuropeptides and other stimuli. The proportion of mast cells that contains chymase and cathepsin G exhibits striking physiological variation in different tissue microenvironments of the lung and airways, with patterns of distribution and levels of production that are hypothesized to vary in lung and airway diseases. This project will explore the regulation of the enzymes at the level of the gene. The level, location and cellular source of chymase and cathepsin G mRNA expression will be explored in normal and inflamed airway tissues, using the quantitative polymerase chain reaction and in situ hybridization. The cis-acting elements on chromosome 14 flanking the closely linked genes for the two enzymes will be defined by transfection of chymase-transcribing cell lines with plasmids containing protease regulatory elements linked to reporter genes. Specific DNA sequences involved in binding to mast cell-specific nuclear regulatory proteins will be defined by DNA footprinting, gel mobility shift, and methylation interference assays. Finally, regulatory proteins involved in mast cell chymase and cathepsin G expression themselves will be isolated and characterized. These studies address basic questions regarding the expression of the biologically important mast cell chymotrypsin-like enzymes and may provide insights into the poorly understood phenomenon of phenotype variation in mast cells of human lung.